patch reads a patchfile which contains output from diff describing changes from an old text file to a new text file. patch then applies those changes to another text file. Typically, you use patch if you are keeping parallel versions of a file. When you make changes to one file, you can use patch to incorporate those changes into other versions of the file.
On Window systems, when this reference page indicates adding a suffix to a file name, patch replaces any suffix with the indicated suffix. Thus, if the original file was hello.c, rather than producing a file hello.c.orig, a file hello.orig would be produced.
If you do not specify either the
If you do not specify a file to be patched and the patchfile is not in context format, patch prompts you for the name of the file you want to patch.
If the patchfile is in context format, patch
tries to determine the file name on its own.
The first two lines of a context patchfile give the names of
the old and new files that diff compared.
If only one of the files exists, patch patches that file.
if neither exists or both do, patch checks for a line
starting with the string Index: and if one exists, obtains
the name of the file to patch from the contents of that line.
Once patch has determined the file to patch, it checks
for an SCCS subdirectory in the current directory and if one exists, it
attempts to obtain an editable version of that file by performing the
SCCS command get
With a context format patchfile, patch can recognize when line numbers given in the patchfile do not match line numbers in the file being patched. Thus it can patch a file with line counts that do not match the old file that was used by diff. To do this, it takes these steps:
- For each section to be changed, patch starts with the line number found in the patchfile, plus or minus any adjustment that must be made for the previous section.
- If the line at this location does not match the line in the patchfile, patch scans forward and backward for a line that does match. If it finds a matching line, patch makes the appropriate changes. patch also remembers the adjustment it had to make to find the matching line, and uses this adjustment in the next section to be changed.
- If patch cannot find a line matching the one in the patchfile, it tries to find the line using the lines given as context. It ignores the first and last lines of the context and searches again. If it finds a match this time, it makes the change and remembers the adjustment.
- If a search ignoring the first and last lines of the context fails, patch searches one more time, ignoring the first two and last two lines of the context. If it finds a match, it makes the changes and remembers the adjustment.
- If patch still cannot find a match, it writes the unmatching portion to the reject file. It then tries to process the next section of changes. Thus the reject file contains the sections that patch is not able to change. Line numbers on sections in the reject file may be different than those in the patchfile, since patch adjusts them using the adjustment that patch calculated for preceding sections.
To some extent, patch tries the same process if the patchfile is in normal rather than context format. Because the patchfile does not contain the context information, patch has less to work with and probably creates more rejects. patch always writes the rejectfile in context format, regardless of the format of the patchfile.
By default, the rejectfile has the same name as the original
file, plus the suffix .rej.
You can use
If you do not specify
The patchfile can contain output from several diff comparisons. patch treats each collection of changes as a separate patchfile, and with each, patch may prompt you for the name of the file to be patched.
saves a copy of the original file in a back-up file. The back-up file name is the name of the original file preceded by the string prefix. If there is already a file with this name, patch overwrites it. When applying more than one patch to the same file, patch only copies the original for the first patch. When you also specify
-ooutfile, patch does not create prefixfile, but if outfile already exists, it creates prefixoutfile. -b
saves a copy of the original file in a back-up file. The back-up file name is the name of the original file plus the suffix .orig. If there is already a file with this name, patch overwrites it. When applying more than one patch to the same file, patch only creates file.orig for the first patch. When you also specify
-ooutfile, patch does not create file.orig, but if outfile already exists, it creates outfile.orig. -c
interprets the patchfile as a context diff file (the output of diff when
-cor -Cis specified). You cannot use this option with -eor -n. -Dsymbol
marks changes with the C preprocessor construct
#ifdef symbol ... #endif
When you compile the resulting (patched) file, you get the original file if symbol is not defined, and the changed file if symbol is defined.
changes the current directory to dir before processing the patch.
specifies the number of lines of a context diff to ignore when searching for a place to install a patch.
forces processing without requesting additional information from the user.
reads information from patchfile. If you do not specify patchfile, patch reads the information from the standard input.
matches any sequences of blanks in the patchfile to any sequence of blanks in the input file. In other words, patch considers two lines equivalent if the only difference between them is their spacing.
ignores any patches which have already been applied. By default, patch rejects already-applied patches.
interprets the patchfile as normal diff output. You cannot use this option with
-cor -e. -ooutfile
writes patched output to outfile instead of the original file. When you specify more than one patch to a single file, patch applies the patches to intermediate versions of the file created by previous patches, resulting in multiple, concatenated versions of the file being written to outfile.
deletes n components from the beginning of all path names in the patchfile. If a path name is an absolute path name (that is, starts with a slash), patch treats the leading slash as the first component of the path, and patch
-p1 deletes the leading slash. Specifying -p0 tells patch to use the full path names given in the patchfile. If you do not specify this option, patch only uses the base name (the final path name component). -R
reverses the sense of the patch script. In other words, patch behaves as if the patch script shows the changes that make the new version into the old version. You cannot use
-Rif the patchfile is in ed script format.
-R, patch attempts to reverse each change recorded in the script before applying the change. patch saves rejected differences in reversed format (which means that you can check the rejections to see if patch made the reversals correctly). -rrejectfile
records rejects in the file rejectfile instead of the default rejectfile name. By default, the rejectfile has the same name as the original file, plus the suffix .rej.
tells patch to remain silent until an error occurs. Normally, patch writes information on the results of the patching process to standard error (stderr).
displays the version number of patch, then exits.
patch may return the following status values:
POSIX.2. x/OPEN Portability Guide 4.0. All UNIX systems. Windows 8.1. Windows Server 2012 R2. Windows 10. Windows Server 2016. Windows Server 2019. Windows 11. Windows Server 2022.
patch was written by Larry Wall.
PTC MKS Toolkit for Power Users
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PTC MKS Toolkit 10.4 Documentation Build 39.